( 667 ) 
but this can only cause starch-formation in a small part. Conversely, 
if only a small part of the area is darkened, the starch-formation 
can be observed at a relatively large distance, but then too little 
carbon dioxide is formed in the small darkened portion to give rise 
to starch-formation in the more distant parts. With this reservation 
an experiment may be mentioned, which was made with the leaf 
of Dahlia (Cactus) Thuringia (exp. LX), with the result, that the 
carbon dioxide can here be carried over through at least 0.5 cm. 
In summarizing his communication, the speaker points out that 
Mr. Zisustra has shown that transport of carbon dioxide is possible 
in all the leaves examined, and that it takes place through the inter- 
cellular spaces. The transport is completely dependent on the size 
and extent of these spaces in the leaf. 
In some parallel-veined leaves, such as those of Hichhornia, Pon- 
tederia and Eucomis, the intercellular spaces are very wide and 
extend in an uninterrupted series throughout the whole length of 
the leaf. By the use of suitable apparatus the leaf base can be made 
to absorb carbon dioxide, which moving on through the intercellular 
spaces by diffusion can give rise to starch-formation a comparatively 
long way off in the leaf apex, when the latter is exposed to light. 
In the great majority of leaves however, carbon dioxide transport 
cannot be shown with the relatively crude apparatus employed. In 
such leaves the carbon dioxide transport can be studied by another 
method, which utilizes the fact that respiratory carbon dioxide, which 
is formed in a darkened and shut off portion of the leaf, can diffuse 
from there through the intercellular spaces to neighbouring lighted 
portions of the leaf and can there cause starch-formation. 
Such leaves possess limited transport areas, which are formed by 
spacious and connected intercellular spaces, and wliich are either 
connected at their margins through much narrower intercellular 
spaces, greatly retarding carbon dioxide transport (Grasses, Acorus, 
Tradescantia) or the areas are completely cut off by veins, which 
have no intercellular spaces (net-veined Dicotyledonous leaves). In 
these leaves with limited transport areas a carriage of carbon 
dioxide over a distance of from 2—3 mm. to at most 2.5 cm. is 
possible. 
Finally the speaker draws special attention to the impossibility of 
carbon dioxide transport being of any advantage to the plant in 
nature, in the first place, because this transport is so extremely 
limited in the majority of cases, and in the second place especially 
because for transport it is necessary that the conducting part should 
not itself assimilate, and also, that the epidermis should be impervious 
